The present invention relates to a push-button switch and, in particular, to a push-button switch having an overload protection function and requiring a manual reset procedure before it is turned on again in case of an overload.
There are many types of push-button switches for various applications. Some comprise a turn-on indicating lamp and others provide an overload protection function. In terms of those with an overload protection function, there are also several kinds of protection principles or mechanisms being adopted. For example, either a blow-out of a fuse wire or a thermal deformation of a bimetallic blade has been adopted as a trigger condition of a switch for overload protection. However, the fuse wire has a disadvantage to reproductibility and thus its usage is gradually phased out. As for the type of switch using a thermal bimetallic blade to perform an overload protection, there have been many kinds of mechanisms proposed, such as those disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,704,594.
In the U.S. Pat. No. 5,786,742, a so-called power cutting member 72 used alternatively to set and to reset the position of a switch is disclosed. In that case, a bimetallic blade 75 is used to push a shaft seat 71 so as to trip and reset automatically a switch. However, the button of the disclosed switch directly depresses under the contact. Thus, the contacts will be kept in its conducting position as an overload is occurring if the button has jammed or pushed by an external force. Moreover, such a switch is not economical due to its use of up to four contacts, (i.e., two sets of contacts) to construct its conduct circuit. The chance of generating arc also increases. Furthermore, such a switch is troublesome to provide a wire connecting the bimetallic blade 75 with the conducting plate 74.
In U.S. Pat. No. 5,223,813, a bimetallic beam 13, a common trip 17 actuated by the bimetallic beam, and a cam member 27 are incorporated with a rocker actuator 33 to perform a contact between contact members 7 and 1. In such a switch, the common trip will be displaced in response to the deformation of the bimetallic beam so as to release the cam member and trip the switch. However, such a switch is rather complicated, even though a jamming of the rocker actuator and an accidental re-push on the switch after an overload can be avoided by virtue of an indirect actuation of its actuator to the common trip. Moreover, a connection of a wire between its cantilever spring 5 and its bimetallic beam 13 is necessary and thus its assembly is also troublesome. Furthermore, a fail-action could possibly happen due to the double-duty of the bimetallic beam to actuate both the rocker actuator 33 and the common trip 17 in case of overload.
In U.S. Pat. No. 4,937,548, a circuit breaker which utilizes the deformation of a thermal actuator 76 to displace a lock lever 62 so as to release a bell crank lever operator 52 is disclosed. In this case, a jamming of its actuator and a re-push on the switch in case of overload is avoided by virtue of an indirect actuation of the actuator to the movable contact 86. However, in such an arrangement it is inconvenient to dispose an indicating lamp. In U.S. Pat. No. 4,661,667, a push-button switch that utilizes a two-hearted-cam locking mechanism to obtain a two-platform locking system is disclosed. However, such a switch is devoid of a protection function as well as a status-indicating function.
A main object of the present invention is to provide a push-button switch having an overload protection function and a low manufacturing cost with a small simple structure ease to assemble.
Another object of this invention is to provide a push-button switch having a sufficient resiliency to perform an instant tripping function at the moment a threshold overload temperature is reached.
Yet another object of this invention is to provide a push-button switch with a simplified structure and assembly by virtue of a combination of a locking mechanism and a bimetallic sheet,
To achieve the objects of this invention, the push-button switch with overload protection comprises:
a housing formed with a button hole, a stem guide, and several terminal holes;
a conducting unit including a first terminal, a second final, a first conducting leaf, and a flat bimetallic sheet;
the first and the second terminals being secured in the terminal holes respectively;
the bimetallic sheet having a movable returning end, capable of deforming from an un-deformed normal position to a deformed overload position in response to overload, and a fixed open end defined by a first leg connected to the first terminal and a second leg to be connected to the first conducting leaf; and
the first conducting leaf being able to move between a closed position in which the second leg of the bimetallic sheet is electrically connected to the second terminal and a normal open position in which the second leg is disconnected from the second terminal; and
an actuating unit installed in the housing and including:
a stem guided by the stem guide and slidably moving between a lower set position and a biased upper reset position
a rocking lever pivotally supported on the stem along a pivoting axle and formed with a nose for depressing the first conducting leaf and a tail opposite to the nose across the pivoting axle;
an enabling rest combined with the rig end of the bimetal sheet and being able to move between a supporting position to support the tail and a withdrawing position to withdraw from the tail, in correspondence with the location of the bimetal sheet in the normal position and the overload position, respectively; and
a lever reseating member for pushing the rocking lever into an idle position in which the tail could be supported by the enabling rest, during a reset course in which the stem moves from the set position to the reset position;
whereby the nose can depress and release the fit conducting leaf so as to make the latter move into the closed position and the normal-open position in response to the movement of the stem to its set position and its reset position, respectively, in case the enabling rest locates in its supporting position, and whereby the first conducting leaf can move to its normal-open position in response to a change of the bimetal sheet into its overload position,
By means of the above structure, even if the stem jams, the switch can still exactly trip at the time overload occurs, and thus an exact overload protection action is obtained. Moreover, by virtue of the special structure of the bimetallic sheet, the structure of the switch can be simplified and thus a structure easy to assemble is obtainable,
In the following, preferred embodiments of the present invention will be described in detail in conjunction with the accompanying drawings.